The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Resistive heating devices, such as tubular heaters, are generally designed to have a predetermined life expectancy and maximum allowable temperature if operated under certain operating conditions. The performance and the life expectancy of the heating devices generally depend on the material properties of the constituent components of the heating devices. When one of the constituent components degrades over time to an unacceptable degree and fails, the entire heating device may fail to function properly. The maximum allowable temperature of the heating device depends on reliability of the constituent components. When one of the constituent components cannot withstand an elevated operating temperature and fail, the entire heating device may also fail.
In addition to the material properties and reliability of the constituent components of the heating device, the life expectancy and maximum allowable temperature of the heating devices are affected by operating conditions and operating modes. For example, the heating devices may have a relatively shorter life expectancy and relatively lower maximum allowable temperature if operated in vacuum environment with low partial pressure of oxygen, or in a rapid ramp-up and ramp-down speed. In view of the various factors that affect performance of the heating device, it is difficult to predict the life expectancy and maximum allowable temperature of the heating devices under a given operating condition.